1. Field of the Invention
The invention generally concerns machined-performed, or automatic, gaging. More particularly, the invention relates to wireless telemetry of gaging data by a workpiece probing device controlled by a machine tool system.
2. Discussion of the Prior Art
Automated or machine controlled gaging of workpieces in machine tool environments optimally is performed by the machine tool system as one of a variety of operations conducted on the workpiece. This, in turn, requires a gaging or probing unit configured for removable retention in a machine tool magazine in the same way as cutting tools are retained therein. Such storage and machine controlled manipulation of the gaging unit also optimally involves wireless tranmission of the data generated by the gaging or probing unit.
The advent of programmable control in machine tool systems has enabled use of such gaging units arranged as touch probes, whereby the machine control program calculates dimensional information concerning a workpiece by determining the location of certain surfaces of the workpiece relative to the coordinates of movement between the machine tool spindle axis and the workpiece. One known touch probe is disclosed in U.S. Pat. No. 4,118,871--Kirkham, and utilizes radio frequency telemetry wherein the touch sensing and transmission function are combined by forming the probe stylus as an antenna whose output is effectively short circuited on contact with the workpiece. Another known touch probe is disclosed in my prior U.S. Pat. No. 4,401,945, and U.S. Ser. No. 478,906 now U.S. Pat. No. 4,578,874 which utilize optical telemetry.
The Kirkham probe suffers the disadvantages of having poor repeatability under conditions where the contacted workpiece may be covered with a nonconductive film, and susceptibility to electromagnetic interference, since the required radio frequency range must be relatively low in order to have an effective short circuit at the probe antenna upon its contact with the workpiece.
My prior infrared telemetry probes and the Kirkham probe may have operability problems in those applications wherein relatively deep workpiece bores or cavities must be probed or gaged, therefore removing the probe transmitting apparatus from line of sight with a remote receiver associated with the machine tool controller. The Kirkham type probe may not operate under such conditions due to the well-known waveguide cut-off effect, wherein the workpiece bore or cavity may be viewed as a waveguide having a cross sectional dimension less than half the wave length of the telemetered signal. At the frequencies required for the Kirkham probe, severe attenuation from the cut-off effect is inevitable for most typical workpiece cavity sizes encountered. The probes of U.S. Pat. No. 4,401,945 and of U.S. patent application Ser. No. 478,906 may or may not work under such conditions, depending upon the strength and direction of reflected optical signals from the probe.